This summer, 12 students from New Hampshire's Dartmouth College are driving across the country in a renovated school bus, called The Big Green Bus, fueled almost entirely on waste vegetable oil culled from fast-food restaurants along the way. The emissions from the bus smell distinctly like the food which the oil cooked earlier, said team leader Andrew Zabel.

"If it's Mexican, you can tell. If it's Chinese, you know. They all have distinct scents," he said. "It is the flavor of the week. You can definitely smell a difference between diesel and grease."

On Monday, the bus made a stop at Cypress Semiconductor, owner of a solar company, SunPower, which donated a 215-watt solar panel that sits on the roof. The panel is there to run the flat-panel TV and the students' iPods and to help get the bus rolling at times. Cypress CEO T.J. Rodgers is a Dartmouth alumnus.

The experiment is a student-led project to bring greater awareness to alternative fuels. The bus is an old Blue Bird school bus that has been slightly modified to run on vegetable oil.

Converting a standard diesel engine to run on vegetable oil is actually relatively simple, Zabel said. First, the group had to install a 120-gallon tank to hold the vegetable oil. Second, vegetable oil, which is more viscous than standard diesel, needs to be heated up to 150 degrees Fahrenheit before it can be run through the engine. To get it to that temperature, the bus initially runs on standard diesel, until the engine fully heats the vegetable oil contained in the tank and tubes.

The SunPower solar panel on the roof also can be used to heat the vegetable oil. "It doesn't work well in cold climates," Zabel explained.

Finally, a filtration system is inserted to keep particulates from clogging the arteries of the engine.

The students started renovating the bus in April. The vehicle has run almost flawlessly for 4,000 miles. The bus gets 8 to 9 miles per gallon of vegetable oil, more than the 7 to 8 miles per gallon that the bus gets on standard diesel.

"We can't figure out why. Waste vegetable oil has about 5 percent less energy," Zabel said. The vehicle can go up to 65 miles an hour.

Vegetable oil releases carbon dioxide and other pollutants into the atmosphere--but less than diesel. Plus, the cost is a lot less, Zabel said. The grease is free.

"We pull over at freeway exits with a plethora of fast-food restaurants," he said. "Any place with a fryolator."

Generally, the students fan out to check out the dumpsters at a rest stop. When one looks promising, they ask the management if they can take their grease.

"At first they are perplexed. The moment of truth comes when we stick the hose into the dumpster and the other end into the gas tank," Zabel said. "That's when they say, 'OK. You are for real.'"

Only occasionally do restaurants refuse. Many have contracts with fat renderers, which take the old grease and sell it to makers of shampoo and cosmetics. These companies refine the fat and resell it for around 90 cents a gallon. Even if the group had to buy their old vegetable oil, Zabel noted, 90 cents a gallon is about a third the cost of standard diesel.

The bus has cruised a good swath of America. Its first stop was the Bonnaroo Music and Arts Festival in Tennessee. Then it was off to Columbus, Ohio; Cleveland; Ann Arbor, Mich.; Chicago; Wisconsin; Seattle; and California. Next it will head to the L.A. area.

Last year, 14 Dartmouth seniors similarly converted a $2,000 bus bought on eBay, but it broke down in Moose Jaw, Saskatchewan. They had to call the dean of students, who wired them $5,000. This year's group of students paid $7,000 for the bus. (Most of the used Blue Birds are sold to Guatemala and Costa Rica, where they are used for public transportation.)

It may seem a little odd to see a "green" experiment coming from Dartmouth, a school that has at times been associated with the conservative political movement and the game "beer pong." But Zabel and SunPower President Dick Swanson said that the environmental movement and big business aren't necessarily at loggerheads.

Alternative energy is already a growing business. Demand for solar panels is growing by 40 percent a year, Swanson said. At the current rate, in 20 years the solar industry could manufacture enough panels to produce a terawatt of electricity a year.

In addition, alternative energies like vegetable oil don't require drilling expeditions and don't come from nations that can be difficult to deal with, Cypress' Rodgers noted.

"The bus shows that something like this is feasible. The next step is to see if it can be made economical" on a larger scale, he said.